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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6335-6340 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The decay of (Ar+3)*→Ar+2+Ar is found to be metastable on a time scale longer than 40 μs. Theoretical considerations are presented for these slow metastable dissociation rates reported in this and other studies. From model calculations it is inferred that tunneling lifetimes from 10−10 to 10 s may be observed.
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1717-1725 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A scaled fundamental equation is presented for the thermodynamic properties of carbon dioxide in the critical region. The equation is constructed by combining earlier experimental pressure data of Michels and co-workers with new specific heat data obtained by one of the authors and represents the thermodynamic properties of carbon dioxide in the critical region at temperatures from 301.15 to 323 K and at densities from 290 to 595 kg/m3.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3215-3223 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of Kr+n (3≤n≤11) cluster ions is observed for the first time in the 565 to 630 nm wavelength range. Kr+3 has a photodissociation cross section of (8.1±0.8)×10−17 cm2 at 612 nm, while Kr+4 and Kr+5 are found to have larger photodissociation cross sections than Kr+3 with a slightly red-shifted spectrum. Only Kr+ is detected as a photofragment of Kr+3, while in the Kr+n (4≤n≤7) experiments, both Kr+2 and Kr+ photofragments are seen. As size n increases from 7 to 11, Kr+ disappears and Kr+3 appears. Laser power studies show that all are single photon photodissociation processes. For higher order Kr+n clusters (4≤n≤7) the intensity ratio between the two photodissociation products Kr+2 and Kr+ is dependent on the wavelength of the laser light used in the photodissociation, but independent of the polarization direction of the laser. Translational energy analysis of the photofragments is used to investigate the photodissociation mechanisms. In contrast to the photodissociation of Kr+3, where two types of Kr+ photofragments with different values of translational energy release are observed, only one type of Kr+2 photofragment, with zero kinetic energy release is found in the Kr+4 photodissociation. These findings are discussed in terms of the dynamics of photodissociation and possible structures of these cluster ions.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5359-5364 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser induced holographic grating relaxation studies of camphorquinone (CQ) diffusing in liner polystyrene (PS) (with both narrow and wide molecular weight distribution) and crosslinked PS (with bis-phenol-A-dimethacrylate as the crosslinking agent) are carried out. Diffusion coefficients of CQ in the polymer hosts are obtained from the decay rate of the intensity diffracted from the laser induced holographic grating. The diffusion coefficients (D) of CQ in polydispersed PS samples are compared with that in nearly monodispersed sample. Diffusion coefficients are found to be equal in both types of polymer samples over the whole temperature range studied, thereby indicating that at high molecular weight the molecular weight distribution has little effect on the diffusion coefficient of CQ. The diffusion coefficient of CQ in crosslinked PS is found to decrease with increasing concentration of the crosslinking agent. It decreases approximately 30 times as the concentration of the crosslinking agent increases to 20%. The relationship between the concentration of the crosslinking agent and polymer free volume is discussed. The diffusion coefficients of CQ in linear and crosslinked PS are also measured as a function of temperature. It is found that the temperature dependence of both D and D/T can be described by a Williams–Landel–Ferry (WLF) equation. However, the WLF constants C1 and C2 differ in both fits. The C2 constant obtained from the D/T vs T fit for linear PS sample agrees with that extracted from the viscoelastic measurement.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4019-4025 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation spectrum of Ar+3 between 520 and 620 nm is reported. A broadband peaking near 520 nm is observed with a cross section of ∼1.8×10−16 cm2 at the peak, in agreement with the findings of Levinger et al. [J. Chem. Phys. 89, 71 (1988)]. However, in the present work, a shoulder whose prominence is highly temperature dependent is observed between 545 and 555 nm. The new results are discussed in terms of various electronic transitions and pathways to dissociation. The photodissociation mechanisms are studied by translational energy analysis of photofragmentation. Three photodissociation mechanisms that involve two electronic energy surfaces are proposed which account for the experimental findings.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 4574-4579 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semi-insulating In0.53Ga0.47As with carrier concentration n=1.2×1012 cm−3, resistivity up to 1090 Ω cm, and mobility up to 9500 cm2/V s at 300 K is grown by liquid-phase epitaxy and doping with Fe. The influence of Fe doping on the photoluminescence of In0.53Ga0.47As is systematically investigated. An acceptor level at Ev+150 meV, tentatively assigned to Fe by some of us earlier, is definitively identified as an Fe-related complex. This acceptor level, however, is not responsible for the semi-insulating behavior of In0.53Ga0.47As as shown by statistical calculations. High-resolution deep-level transient spectroscopy experiments show two deep acceptors at EC−ET=0.44 and 0.30 eV, respectively. The first one, which dominates, is identified as being caused by the Fe3+/Fe2+ acceptor level. The second, somewhat weaker one, might be caused by the O-related trap recently discovered by Loualiche et al. [Appl. Phys. Lett. 51, 1361 (1987).] Combining the Fe acceptor energy position in In0.53Ga0.47As with its known value in InP and the known conduction-band discontinuity of the InP/In0.53Ga0.47As heterointerface we find that the vacuum referred binding energy model is approximately but not strictly valid. In this model the transition-metal impurity levels are aligned with respect to the vacuum level across interfaces regardless of the surrounding host crystal environment.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3589-3592 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The measurements of x-ray diffraction, the temperature dependence of the dc resistance and the ac susceptibility have been performed for the single-phase 3D-metal doping systems YBa2 Cu3−x Mx Oy (M=Fe, Co, and Ni; x=0.025, 0.05, 0.075, 0.10, 0.25, and 0.50 for Ni and Co and 0.05, 0.075, 0.10, 0.15, and 0.20 for Fe). With an increase of impurity content, two structural transitions were observed for the Co and Fe dopants but only one for the Ni dopant. The resistivity in the normal state changes from metallic to semiconductinglike behavior and the depression of Tc is linear with the impurity concentration (x) when x〈0.10. A weak Curie–Weiss type paramagnetism, which is enhanced with impurity content, exists in the samples studied. Incorporating other work on oxygen defects, we suggest that a change of oxygen content induced by doping was the dominant effect on superconductivity in these samples.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 181-186 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defects in GaN grown using metalorganic chemical vapor deposition were studied through the use of monoenergetic positron beams. For Mg-doped GaN, no large change in the diffusion length of positrons was observed before and after activation of Mg. This was attributed to the scattering of positrons by potentials caused by electric dipoles of Mg–hydrogen pairs. For Si-doped GaN, the line-shape parameter S increased as carrier density increased, suggesting an introduction of Ga vacancy due to the Fermi level effect. Based on these results, we discuss the effects of the growth polar direction of GaN on optical properties in this article. Although the optical properties of a GaN film grown toward the Ga face direction exhibited excitonic features, a film grown toward the N face (−c) direction exhibited broadened photoluminescence and transmittance spectra, and a Stokes shift of about 20 meV was observed. This difference was attributed to extended band-tail states introduced by high concentrations of donors and acceptor-type defects in −c GaN. © 2001 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3619-3621 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the pattering of sp3- and sp2-bonded carbon by using conducting atomic-force microscopy (AFM) working in the noncontact mode. A ta-C film with ∼80% sp3 bonds was scanned by the conducting AFM with a biased tip. A current image that clearly shows gray/white and black features was obtained while scanning in the noncontact mode. These features were proposed to be the result of the different electron emission abilities of the sp3- and sp2-bonded carbon in the film. The result not only enables us to image the distribution of the sp3 and sp2 bonds of a-C, but also extends the AFM to provide the electron emission information of a-C on a nanometer scale. © 2001 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6974-6976 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization measurements on the Heusler alloy Co2ScSn show that the system undergoes a transition from a paramagnetic state to a possible helimagnetic state at Tc=238 K, and exhibits spin-glass behavior below 100 K. 119Sn Mössbauer spectra of Co2ScSn are found to be influenced significantly by heat treatment. Single-dip spectra are observed above Tc as expected from the cubic symmetry at the Sn sites. The transferred hyperfine field at the Sn nuclei appears below Tc, increases with decreasing temperature, and has a value of 38 kOe at 4.2 K. The temperature dependence of the hyperfine field at the Sn nuclei shows a small break at 100 K which correlates with the onset of the spin-glass transition.
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